An apparatus for making a reinforced fabric ribbon such as a tire ply is disclosed in prior U.S. Pat. No. 3,803,965. As shown in FIGS. 3-9 of that patent, a number of laterally spaced reinforcing wires are moved through a crosshead extrusion die having grooved matching die plates for guiding the wires accurately in uniformly spaced relation. The extrusion die is provided with passageways for flowing the elastomeric material under pressure around and encapsulating the wires as they emerge from the guide grooves, thus producing the reinforced ribbon of uncured fabric. The ribbon is then severed into lengths which may be oriented at a preselected bias and stitched edge to edge to produce a belt of fabric with the reinforcing wires at the preselected bias to the length of the belt.
It is very important that the uniform lateral spacing of the wires or filaments in the extruded reinforced ribbon be accurately maintained, because during the manufacture of a tire utilizing increments of such ribbon as a ply or plies therof the fabric is expanded laterally of the filaments to almost twice its original width, with the result that if the spacing is uneven, the wider spaces become weakened areas.
It has been found in practice in using extruding dies such as shown in said U.S. Pat. No. 3,803,965, wherein the elastomeric material is flowed under pressure across the top and bottom of the wires as they emerge from the guide grooves, that the resulting ribbon is often weakened, apparently because the uniform spacing between the wires is not maintained. On expansion during tire building, the wider spaces produce weak spots or areas and in some cases the adhesion between the elastomeric material and the contiguous wires is materially reduced.
A number of variations have been proposed in the design of the extrusion die and of the throat wherein the elastomeric material is flowed around the wires emerging from the guide grooves, but in all cases of which I am aware, the difficulties causing weakened areas in the extruded reinforced ribbon have not been overcome.